1. Field of the Invention
The present invention relates to a sheet processing apparatus that processes a sheet bundle formed of a plurality of sheets, and an image forming apparatus that includes the sheet processing apparatus.
2. Description of the Related Art
In the past, as an image forming apparatus for forming an image on a sheet, there is an image forming apparatus where a sheet processing apparatus is provided in an apparatus main body for forming an image on a sheet.
As a sheet processing apparatus, there is a sheet processing apparatus that has a function to bind a sheet bundle in the form of a booklet (see U.S. Pat. No. 6,276,677). As illustrated in FIG. 18, the sheet processing apparatus feeds sheets, which are fed from an apparatus main body 900A of an image forming apparatus, to a gap between a driver 18 of a stapler 40 that protrudes a staple and an anvil 19 that bends the staple, one by one. Then, an end stopper 23 receives the sheet. The end stopper 23 waits at a position where a portion to be bound (generally, a middle portion in a longitudinal direction) of the sheet may face the stapler.
A sheet is nipped between conveying rollers 17a and 22a and leaf springs 17d and 22d that press the sheet against the conveying rollers 17a and 22a, and is conveyed by the rotation of the conveying rollers 17a and 22a. When a predetermined number of sheets are received by the end stopper 23 and form the shape of a bundle, the bundle is bound by the stapler 40. After that, the end stopper 23 is lowered while receiving the lower end of the bound sheet bundle, and the bound portion of the sheet bundle faces a protruding plate 25a. After that, the protruding plate 25a pushes the sheet bundle and tucks the sheet bundle into a nip between a pair of folding rollers 26 and 27. The pair of folding rollers 26 and 27 conveys the sheet bundle while folding the sheet bundle, and discharges the sheet bundle to a tray 32. The discharged sheet bundle is formed in the shape of a booklet.
However, in a sheet processing apparatus 2 in the related art, unless an end stopper 23 reliably receives sheets which are fed in a vertical direction, the ends of the sheets are not aligned. For this reason, the sheet is made to bump into the end stopper 23 by the conveying forces of the conveying rollers 17a and 22a. Meanwhile, the conveying forces are determined depending on the elastic forces of the leaf springs 17d and 22d that press the sheet against the pair of folding rollers 26 and 27 and the conveying rollers 17a and 22a. If the elastic force is increased, the conveying force is increased.
For this reason, even though the elastic force is adjusted so that an appropriate conveying force is obtained, as illustrated in FIG. 19, a thin sheet or a sheet S longer than the distance X between the conveying roller 22a and the end stopper 23 has been bent and buckled while bumping into the end stopper 23.
There is a concern that the sheet processing apparatus in the related art may process a sheet having low stiffness, a thin sheet, or a sheet longer than the distance between the stapler 40 and the end stopper 23 while buckling occurs as described above. For this reason, the sheet processing apparatus in the related art has been subject to the limitation of the length, thickness, and stiffness of a sheet to be processed.
Further, an image forming apparatus, which includes the sheet processing apparatus in the related art in the apparatus main body thereof, should form images on sheets again as much as sheets that are processed while buckling occurs. For this reason, image forming efficiency is low.
The invention provides a sheet processing apparatus that suppresses buckling occurring on a sheet to be processed, and processes a sheet without having the limitation of the length, thickness, and stiffness of a sheet to be processed.
The invention provides an image forming apparatus including a sheet processing apparatus, which processes a sheet while suppressing buckling occurring on a sheet, and suppresses the forming of images again.